Two other men, aged 28 and 29, were rescued by emergency services and taken to Westmead Hospital with leg injuries.

SafeWork NSW investigators returned to the site on Friday to work out exactly what happened, a spokesman said.

"Initial inquiries indicate the mixer activated while two workers were undertaking maintenance on the tank. A third worker, aged 28, is reported to have gone to their assistance and been injured," the spokesman said.

"A 29-year-old worker that was undertaking maintenance on the tank was freed by emergency services while the other worker, aged 42, was trapped by the mixer's blade and passed away from injuries he sustained."

SafeWork engineering experts were inspecting the mixer to work out the cause of the incident, and NSW Police were also preparing a report for the coroner.

NSW Minister for Innovation and Better Regulation Matt Kean said the death was "totally unacceptable".

"No worker should go to work and be injured on the job, let alone lose their life," he told Nine News.

"We will do whatever is necessary to get to the bottom of what's gone on, and hold those responsible to account."

On Thursday, NSW Ambulance Superintendent Paul Turner said the death was a tragedy.